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Crash Course Electronics/Capacitors (view source)
Revision as of 10:00, 10 February 2012
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Obviously metal plates don't care about polarity as they are almost identical and so can be interchanged without anyone noticing a difference. | Obviously metal plates don't care about polarity as they are almost identical and so can be interchanged without anyone noticing a difference. | ||
These were pretty large capacitors | These plate capacitors were physically pretty large capacitors but their capacitance is pretty low. | ||
To save space and increase capacitance the 2 plates can be made of metal foil and the air can be replaced by an electrically insulating layer | To save space and increase capacitance the 2 plates can be made of metal foil and the air can be replaced by an electrically insulating layer in between. To save even more space the foils can be rolled into a tube. ([http://wiki.4hv.org/index.php/Rolled_foil_capacitor_-_60_kV,_3.5_nF Insctruction] to create your own capacitor of foil) This cylindric form of foil capacitors was very common for a long time -but nowadays foil capacitors are mainly rectangularly shaped blocks. There are still few current foil capacitors which are cylindrical - but most of today's cylindrical capacitors are of an other kind (the elctrolytic capacitor, see next section about polarized capacitors). | ||
An other type of an unpolarized capacitor is the ceramic capacitor. Here the plates are insulated by ceramics instead of foil - increasing the capacity and maximum voltage rating. [ | An other type of an unpolarized capacitor is the ceramic capacitor. Here the plates are insulated by ceramics instead of foil - increasing the capacity and maximum voltage rating. [[wikipedia:Ceramic capacitor|Images on wikipedia]] | ||
=== capacitors where polarity matters === | === capacitors where polarity matters === | ||
Electrolytic capacitor: | Electrolytic capacitor: | ||
This kind of capacitor needs to be connected in the correct polarity or it will be destroyed. (There are spectacular videos on youtube of explosions occuring when connected to reversed polarity). They are basically cans of aluminium filled with an electrolytic fluid. The two plates are gone, but are replaced: one "plate" now is the electrolytic fluid, the other one is the can. Between the can and the fluid a thin isolating layer exists so they don't connect - like the foil in the foil capacitor. As the 2 "plates" are no more identical like the metal plates were in the foil capacitor the symbol also changes: one side is thicker or bent and no more similar to the other. However there are also symbols where only a + or - sign marks one side of the capacitor. Have a look at the [ | This kind of capacitor needs to be connected in the correct polarity or it will be destroyed. (There are spectacular videos on youtube of explosions occuring when connected to reversed polarity). They are basically cans of aluminium filled with an electrolytic fluid. The two plates are gone, but are replaced: one "plate" now is the electrolytic fluid, the other one is the can. Between the can and the fluid a thin isolating layer exists so they don't connect - like the foil in the foil capacitor. As the 2 "plates" are no more identical like the metal plates were in the foil capacitor the symbol also changes: one side is thicker or bent and no more similar to the other. However there are also symbols where only a + or - sign marks one side of the capacitor. Have a look at the [[wikipedia:Electrolytic capacitor#Polarity|wikipedia page]] for its symbols. | ||
An other form of a polarized capacitor is the tantalum capacitor ([ | An other form of a polarized capacitor is the tantalum capacitor ([[wikipedia:Tantalum capacitor|image]]). They can easily be confused with [[wikipedia:Ceramic capacitor|ceramic capacitors]] which often come in a similar looking case. But their much larger capacitance can be used as a hint that it's not a ceramic capacitor: | ||
Ceramic capacitors are in the range of pF to few nF - tantalum capacitors range from several approx. 100 nF to several µF. | Ceramic capacitors are in the range of pF to few nF - tantalum capacitors range from several approx. 100 nF to several µF. | ||
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Capacitance varies when different materials are inserted or removed between the 2 plates of a capacitor. For example the capacitance increases when air is replaced by a dielectric (like the plastic foil of the foil capacitor or other insulators). | Capacitance varies when different materials are inserted or removed between the 2 plates of a capacitor. For example the capacitance increases when air is replaced by a dielectric (like the plastic foil of the foil capacitor or other insulators). | ||
In old radios variable capacitors with a rotary knob are found that look similar to a potentiometer. You can recognize plastic foils and thin metal plates which move when the knob is turned. ([ | In old radios variable capacitors with a rotary knob are found that look similar to a potentiometer. You can recognize plastic foils and thin metal plates which move when the knob is turned. ([[wikipedia:Variable capacitor|Example images on wikipedia]]) | ||
== Typical usage of Capacitors == | == Typical usage of Capacitors == | ||
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* Aging effects not as strong as electrolytics but more than film (brittle ceramics materials, can have water in the ceramic substrate) | * Aging effects not as strong as electrolytics but more than film (brittle ceramics materials, can have water in the ceramic substrate) | ||
* small piezo-electric effect: you can hear your audio or other signals in the capacitor at high frequencies and high voltage levels. | * small piezo-electric effect: you can hear your audio or other signals in the capacitor at high frequencies and high voltage levels. | ||
== Links == | |||
Calculate lowpass filter (using a capacitor and a resistor, german):<br> | |||
http://www.elektrotechnik-fachwissen.de/wechselstrom/rctp.php | |||
Measure capacitance using Arduino:<br> | |||
http://arduino.cc/it/Tutorial/CapacitanceMeter | |||
[[Category:Electronics]] | [[Category:Electronics]] | ||
[[Category:Martin Schied]] | [[Category:Martin Schied]] | ||